Small fixes to extensions managed storage documentation.

Makes a number of small changes to the documentation on configuring apps
and extensions by policy, which relates to the managed storage area:

- Updates links to documentation and code samples.
- Provides a link to the schema associated with the example policy.
- Fixes some bash commands.
- Clarifies that policies need to be manually reloaded, since the sync interval seems to be significantly reduced.

Bug: N/A
Change-Id: I528754dad849d724a366dd7aed0ae7283d4320a6
Reviewed-on: https://chromium-review.googlesource.com/c/website/+/6612423
Reviewed-by: Fr <beaufort.francois@gmail.com>
Reviewed-by: François Beaufort <fbeaufort@google.com>
Commit-Queue: Oliver Dunk <oliverdunk@chromium.org>
Reviewed-by: Daniel Cheng <dcheng@chromium.org>